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Volume 9, Issue 3

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WaveX: Extracting Wavelets from Seismic Data
John M. Novak

The Problem

Petroleum exploration employs a variety of methods for characterizing the earth's subsurface while seeking potential hydrocarbon reservoirs. One of the most common techniques used on land is to create vibrations on the surface, perhaps by a dynamite explosion, then to listen via an array of geophones for echoes from beneath the surface. This and associated technologies are collectively called seismic exploration.

The seismic data recorded by the sensors around the explosion are processed and massaged to extract meaningful signals, which may be visualized as an image of the subsurface. These images can then be analyzed with the goal of understanding something about the structure of the earth, such as the types and nature of the rock and whether fluids, such as oil or gas, exist within pores in the rock.

One way to calibrate the seismic data gathered at the surface with the properties of the earth is to drill a hole, or well, into the earth. We can more directly measure the characteristics of the earth at that point. This information can then be compared to the seismic data, a process called a well tie. Tying the well involves matching correlative events observed in the well (or the well log, typically acoustic velocity and bulk density measurements) with the seismic data. This process generates a waveform whose features can be used to assess and adjust the seismic data. This waveform is called a wavelet. (The wavelet is not the same as the mathematical structure of the same name.) The character of the extracted wavelet can also provide feedback about the quality of the well tie.

Commercial software used for tying wells and extracting wavelets imposes certain algorithms and methodologies upon the user. GMG/AXIS Geophysics desired a more flexible tool that could be modified to suit the peculiarities of individual data sets and could be adapted to different algorithms. Mathematica appeared to be an effective platform on which to create this tool.



     
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